Synthesis and characterization of soluble polyimides functionalized with carbazole moieties

Here, we report the synthesis and characterization of new soluble polyimides that are functionalized using carbazole moieties in their side chain. As a monomer for synthesizing the polyimides, 4″‐carbazole‐9‐yl‐[1,1′;2′,1″] terphenyl‐4‐4′‐diamine and 2‐(3‐carbazol‐9‐yl‐propyl)‐biphenyl‐4,4′‐diamine were synthesized and then characterized using ¹H NMR, ¹³C NMR, FTIR, UV–visible and photoluminescence spectroscopy, differential scanning calorimetry (DSC), and elemental analysis. The polyimides synthesized via chemical imidization processes were characterized with X‐ray photoelectron spectroscopy, gel permeation chromatography, wide angle X‐ray diffraction, thermogravimetric analysis, DSC, tensile strength measurement, and dielectric property measurement. Results showed that the synthesized polyimides were soluble in a variety of organic solvents, optically transparent in a visible range, thermally stable, mechanically strong, and considerably low dielectric. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8117–8130, 2008     

On the correlation between the magnetic structure and the electrical properties of EuB6

Single crystals of EuB₆ were prepared by the floating-zone method. Magnetic and electric measurements on these crystals in the temperature range 1.6–300 K revealed that the pure EuB₆ is an antiferromagnet with a Néel temperature of 5–6 K and has a carrier concentration of 4.2 × 10²⁰ cm^-3. It was found that in polycrystalline sample, defects of Eu ions reduce the carrier concentration and make the sample ferromagnetic. It is suggested that the conduction electrons in pure EuB₆ originate from the overlap of the 4f band tail and the conduction band.     

The algebraic degree of geometric optimization problems

In this paper we apply Galois methods to certain fundamentalgeometric optimization problems whose exact computational complexity has been an open problem for a long time. In particular we show that the classic Weber problem, along with theline-restricted Weber problem and itsthree-dimensional version are in general not solvable by radicals over the field of rationals. One direct consequence of these results is that for these geometric optimization problems there existsno exact algorithm under models of computation where the root of an algebraic equation is obtained using arithmetic operations and the extraction ofkth roots. This leaves only numerical or symbolic approximations to the solutions, where the complexity of the approximations is shown to be primarily a function of the algebraic degree of the optimum solution point.     

Binding energies of excitons in ionic quantum well structures

Il Nuovo Cimento D - We have calculated the binding energies of excitons in quantum well structures based on ionic semiconductors by including the electron-hole interactions with the...     

The electroweak mixing angle in unified gauge theories—the renormalisation effects

A general analysis of the renormalisation corrections to the unification results for the coupling constants of strong and electroweak interactions is attempted. In particular, the effects of introducing an energy scale intermediate between the unification energy and the low-energy regions are studied and found to be important. This analysis is applied to unification schemes of both kinds, namely, unification at superhigh energies, and unification at accessible energies.     

Microestimation of explosives present in different compositions

Summary High explosives having the sameR _f values on a thin-layer chromatogram and difficult to separate are readily resolved as their coloured -complexes with aromatic amines. After liberation from their complexes on the plate, up to 1.5 g of the explosives can be conveniently estimated at their characteristic absorption maxima.

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Zusammenfassung Hochexplosive Substanzen mit gleichenR _f -Werten auf Dünnschichtchromatogrammen, die sich schlecht trennen lassen, werden als gefärbte -Komplexe mit aromatischen Aminen gut voneinander getrennt. Nach Freisetzung aus den Komplexen auf der Platte können bis zu 1,5 g der Explosivstoffe bei ihrem charakteristischen Absorptionsmaximum auf übliche Weise bestimmt werden.

     

Wave propagation in a rarefied plasma with finite Larmor radius

Wave propagation in a rarefied two-component plasma immersed in a uniform constant magnetic field has been discussed wherein the plasma pressure is assumed to be anisotropic owing to finite Larmor radius effect. It is shown that, for propagation along the external magnetic field, there exist two modes of wave propagation, namely, the gravitational mode and the hydromagnetic mode. The former is found to be independent of the magnetic field and hence of the Larmor radius, while the latter is appreciably influenced by the finite Larmor radius. On the other hand, for transverse propagation, there are three modes of wave propagation viz. the ion-sound mode, the electron-sound mode and the electromagnetic mode. It is shown that only the lowfrequency ion-sound mode is affected by the finite Larmor radius.     

Deconvolution of the light- and heavy-hole free exciton fine structure in AlxGa1−xAs---GaAs multi quantum wells using photoluminescence excitation spectroscopy

Sharp-line structure associated with both the light-hole free exciton (LHFE) and heavy-hole free exciton (HHFE) transitions has been observed in multi-quantum-well (MQW) structures of four well sizes in photoluminescence (PL) and reflection spectra. These spectra have been deconvulated using photoluminescence excitation spectroscopy (PLE). The LHFE and HHFE sharp-line structure is associated with interface structure composed of growth islands at the interface between the barriers and the wells. Estimates of the average interface island sizes for the four different MQW structures are made based on theoretical modelling. A correlation is established between particular LHFE fine structure components and specific HHFE fine structure components. A model is developed to account for the LHFE and HHFE fine structure based on a non-random distribution of the interface structure. The physical location of the excitons is demonstrated to be in regions of the wells with essentially identical interfacial microstructure. Evidence for diffusion of excitons from effectively narrow well regions to wider well regions is presented.     

The stereochemistry of guggulsterol-1

The steroechemistry of guggulsterol-1, a component of the exudate of $\text{Commiphora}$$\text{mukul}$, is shown to be 20(R), 22(R)($\text{3}$).     

Specific Molecular Interactions of Dihydropyridine Moiety in Polar and Non-Polar Solvents at Various Concentrations and Temperatures 303–318 K on Ultrasonic Data

Russian Journal of Physical Chemistry A - Ultrasonic studies of compounds of dihydropyridine series in polar and non-polar solvents at various concentrations and temperatures 303–318 K....